Thermostat with a permanent magnet snap switch



T. E. LARSEN Fgb. 23, 1965 THERHOSTAT WITH A PERMANENT MAGNET SNAP SWITCH INVENTOR.

THEODORE E. LARSEN Filed Oct. 17. 1960 W ATTORNEY United States Patent 3,171,003 THERMOSTAT WITH A PERMANENT MAGNET SNAP SWITCH Theodore E. Larsen, Minneapolis, Minn., assignor to Honeywell Inc., a corporation of Delaware Filed Oct. 17, 1960, Ser. No. 63,150 4 Claims. (Cl. 200-138) The present invention is concerned with an improved temperature responsive control device; in particular, .a bimetal operated switching device has a switch operator comprising a permanent magnet with a variable reluctance shunt for changing the operation differential of the device.

While the use of adjustable shunts on electric magnetic actuators is recognized as being old, the present invention is concerned with a temperature responsive switch actuator which has a magnetic circuit for varying the differential of the switch. A movable member attached to the output of the temperature responsive device is moved against a permanent magnet to actuate the switch. Attached to the magnet is a ferromagnetic member which cooperates with the movable member to complete a magnetic circuit. By movement of the ferromagnetic member, the reluctance of the magnetic circuit is changed by varying the length of the air gap between the ferromagnetic member and the first mentioned movable member.

An object of the present invention is to provide an improved temperature responsive switch device having two members pulled together by magnetic attractionso one member moves a switch member against the other member to close an electrical circuit.

Another object of the present invention is to provide a magnetic temperature control switch device which has a variable differential; that is, the difference between the temperature at which a switch makes and the temperature at which the switch breaks is changed by changing the reluctance in a magnetic circuit.

These and other objects of the present invention will become apparent upon a study of the specification and drawing of which:

FIGURE 1 is a front view of the control dew'ce with the cover removed.

FIGURE 2 is a side sectional view of the control de vice looking from the left of FIGURE 1.

FIGURE 3 is a prospective view of the magnetic portion of the switch operator with the electrical switch.

Referring to FIGURE 1, a base or housing is shown with a pair of ears 11 and 12 for attaching the housing to the inside surface of an outer casing of a furnace or unit heater. A spiral bimetalor temperature responsive device 13 has one extremity attached to an adjustable shaft 14 mounted to the housing 10. The position of shaft 14 can be changed by moving a lever 15 which is attached to the shaft. Lever 15 has a gear sector at one end which engages a gear attached to a control knob shaft '21 also adjustably mounted on base 10. Lever 15 is biased in a counter clockwise direction by the force of a spring 22 which is attached between the housing 10 and other extremity 23 of lever 15. Theposition of shaft 14 is adjusted by rotating a control point adjusting knob 24 as shown in FIGURE 2 which is attached to shaft 21 outside a housing cover 16. A member 25 also attached to shaft 21 provides a means for limiting the total angle of movement of shaft 21 to an angle determined by limit stops (not shown).

A ferromagnetic member is attached to other extremity 31 of bimetal 13. Member 30 is moved to the left or right as shown in FIGURE 1 depending upon the temperature of bimetal 13. Insulatingly attached to the base or housing is a bracket 32. Bracket 32 provides a physical mount for a portion of a switch operator as well as an electrical terminal which is connected to a wire 33. The upper end of bracket 32 has a shaft 34 attached thereto. Shaft.

extends along a side of the magnet parallel to the shaft to have an extremity projection flush with the left hand face of the magnet. The member 42 is mounted on shaft 34 for rotation about the shaft. A spring type disc 44 is interposed between the magnet assembly 40and col-' lar 35 to add some friction to the movement of member 42 about shaft 34.

Interposed between ferromagnetic member 30 and mag net assembly 40 is flexible blade 50 which contacts the left hand end of shaft 34' or a silver contact 61 projecting to the left of magnet assembly 40 to form a switch. When the switch is closed, a circuit is provided between wire 33' and a wire 51 since flexible blade 50 is attached to housing 10 by a screw 52 which is electrically insulated from the housing and provides a connection terminal for wire 51. Member 30 is covered with tape or some suitable electrical insulating material 60. When member 30 moves against the magnet assembly to push flexible blade 50 against the left hand end of shaft 34 or stationary contact 61, member 30 as well as the bimetal and other parts mounted on housing 10 are electricaily'insulated from blade 50.

The force developed between magnet assembly 40 and member 30 depends upon the reluctance of the magnetic circuit which includes ferromagnetic members 42'and 30.

The air gap between end 43' of member 42 and member 30 can be varied by rotating member 42'about shaft 34. A notch 62 is provided in member 42 so a screw drivercan be used to rotate member 42 and change the gap in the magnetic circuit.

Referring to FIGURE-'2, bimetal 13 is mounted adjacent an indented portion 65 of housing 10. The outer side of the indented portion 65 is painted black so heat from the furnace will be'absorbed by the housing to influence the temperature of bimetal 13.

The flexible blade 50 has two fingers 70 and 71 as shown in FIGURES 2 and 3 projecting upward from the portion attached to the housing by screw 52. The fingers distribute the load on member 30. As member 30 moves to the right as shown in FIGURES 1 and 3'under the power of bimetal 13, little force is necessary to move one or bothof the flexible blade fingers against the stationary contact 61.

Referring to FIGURE 1, another projection 73 which is attached to lever 15 provides a means to remove member 30 away from magnet assembly 40 to positively open the switch. By rotating knob 24 counter clockwise, pro ection 73 moves clockwise to engage the upper end of member 30 to move itaway from flexible blade 50 allowmg the flexible blade to move away from contact 61.

Operation As shown in FIGURE 1 the control device is in the off positionand the switch provides an open 'circuit be tween wires 33 and 51. By the adjustment of the position of shaft 14, the control point of the device is selected. Knob 24 can be turned clockwise to increase the control point of the device by repositioning shaft 14 in a counter clockwise direction. Spring 22 provides a force to maintain the engagement of gear teeth between lever 15 and shaft 21. The resistance to movement of lever 15 is provided by the frictional attachment of shaft 21 to the housing as shown in FIGURE 2.

As the temperature drops, the bimetal moves member to the right. As member 30 comes within a predetermined distance of magnet assembly 40, member 30 will snap agairistthe magnet assembly to push the flexible blade 50 against fixed contact 61. As the bimetal 13 heats up due to the heat being received from the furnace, a force is providedon member 30 to the left. The force must be built up sufficiently to overcome the magnetic attraction of magnet assembly before the switch will operate.

In order to vary the temperature difference between the temperature required to move member 30 against the magnet assembly and the temperature required to move the member 30 away, the position of member 42 with respect to member 30 is changed. The rotation of member 42 about shaft 34 changes the length of the air gap between end 43 of member 42 and member 30. The change in the length of this air gap varies the magnetic reluctance of the magnetic circuit and thus the force available to pull member 30 to the right; and also the force necessary to pull member 30 away from the magnet assembly 40 to the left.

When member 30 moves to the right against the magnet assembly, the fingers 70 and 71 of the flexible blade are moved toward the contact 61. An electrical circuit is provided even though only one of the fingers 70 or 71 engages contact 61.

While the present invention has been described as a bimetallic operated temperature control device, the intention is to limit the scope of the invention by the appended claims in which I claim:

1. In a thermostat, a base, a bimetal, said bimetal having one end adjustably mounted on said base whereby the position of the bimetal can be changed to select a predetermined control point, a first ferromagnetic member attached to a free end of said bimetal, a bracket electrical- 1y insulated from and attached to said base, a shaft attached to said bracket as an integral part thereof, a magnetic assembly adjustably mounted on said shaft so said assembly can be rotated about said shaft, said assembly comprising a permanent magnet and a second ferromagnetic member having one end attached to one pole side of said magnet extending along one side of said magnet and having another end projecting beyond the face of the other pole of said magnet, and a flexible switch blade forming a movable contact member of a switch when said blade engages an end of said shaft extending beyond said face of said magnet which forms a fixed contact of said switch, said blade being interposed between said first magnetic member and said face of said magnet whereby upon the movement of said first member toward said magnet said switch is closed when said member is attracted against said magnet, said assembly being effective to change the differential temperature of said bimetal, which is necessary to bring about switch operation, by rotating said second member to increase the air gap between said another end of said second member and said first member.

2. In a thermostat, a housing, a bimetal, said bimetal having one end adjustably mounted on a side of said housing whereby the position of the bimetal can be changed to select a temperature control point, said housing having an outside portion of one side painted black so radiant heat from outside said housing will more effectively heat said bimetal, a first ferromagnetic member attached to said bimetal to be moved thereby, a switch means comprising a fixed member electrically insulated from and at- 65 tached to said base, and a movable member electrically insulated from and attached to said base, said fixed and movable member being adapted to be connected into an electrical control circuit, and a magnetic assembly adjustably mounted on said fixed member, said assembly comprising a permanent magnet and a second ferromagnetic member forming a portion of a low reluctance magnetic path between the poles of said magnet, said movable member being interposed between said first magnetic member and said magnetic assembly whereby upon the movement of said first member toward said magnet said switch is closed when said first member is attracted against said magnet, said first member when in a switch closing position forming the remaining portion of said low reluctance path, said assembly being effective to change the differential temperature of said bimetal which is necessary to bring about switch operation by changing the position of said second member with respect to said first member and thereby change the reluctance of said magnetic path.

3. In a thermostat, a base, temperature responsive means connected to said base, a control knob having a shaft attached to said base and connected to adjust the position of a free end and thus the control point of said responsive means, a first member attached to said free end of the responsive means for movement as the temperature of said responsive means changes, a second member connected to said base to be engaged by said first member, switch means adapted to close an electric circuit, said switch means comprising a movable member having one end attached to said base to be pivotally mounted and positioned between said first and second members to form a closed circuit with said second member when said first and second members are together, magnetic means connected to one of said first or second members, the other of said first or second members being ferromagnetic, and a ferromagnetic shunt attached to said magnetic means whereby the effect of said magnetic means can be changed to vary a temperature differential needed to open and then close said switch means.

4. In a thermostat, a base, temperature responsive means connected to said base, a first member attached to a free extremity of said responsive means for movement as the temperature of said responsive means changes, a second member connected to said base and forming one side of a circuit, and switch means adapted to close an electric circuit, said switch means comprising at least one'flexible blade connected at one end to said base to form another side of the circuit and having a free end interposed between said members to form a closed circuit when said blade engages said second member, one of said members being made of a magnetic material and the other of said members being made of a ferromagnetic material whereby said first and second members are magnetically attracted to one another when said first member is moved within a predetermined distance of said second member by said temperature responsive means.

References Cited by the Examiner UNITED STATES PATENTS 142,486 9/73 Little 200-87 1,020,881 4/ 12 North ZOO-90 2,180,701 11/39 Wilson 200-l22 2,519,025 8/50 Crise 200-87 2,835,766 5/58 Few 200138 2,855,484 10/58 Kreuter 200-138 FOREIGN PATENTS 600,250 4/48 Great Britain.

ROBERT K. SCHAEFER, Acting Primary Examiner.

MAX L. LEVY, ROBERT K. SCHAEFER, BERNARD A. GILHEANY, Examiners, 

1. IN A THERMOSTAT, A BASE, A BIMETAL, SAID BIMETAL HAVING ONE END ADJUSTABLY MOUNTED ON SAID BASE WHEREBY THE POSITION OF THE BIMETAL CAN BE CHANGED TO SELECT A PREDETERMINED CONTROL POINT, A FIRST FERROMAGNETIC MEMBER ATTACHED TO A FREE END OF SAID BIMETAL, A BRACKET ELECTRICALLY INSULATED FROM AND ATTACHED TO SAID BASE, A SHAFT ATTACHED TO SAID BRACKET AS AN INTEGRAL PART THEREOF, A MAGNETIC ASSEMBLY ADJUSTABLY MOUNTED ON SAID SHAFT SO SAID ASSEMBLY CAN BE ROTATED ABOUT SAID SHAFT, SAID ASSEMBLY COMPRISING A PERMANENT MAGNET AND A SECOND FERROMAGNETIC MEMBER HAVING ONE END ATTACHED TO ONE POLE SIDE OF SAID MAGNET EXTENDING ALONG ONE SIDE OF SAID MAGNET AND HAVING ANOTHER END PROJECTING BEYOND THE FACE OF THE OTHER POLE OF SAID MAGNET, AND A FLEXIBLE SWITCH BLADE 